DC-to-DC converters, such as buck-boost converters, with high power conversion efficiency are widely used as one of the typical switching power supplies. A known control apparatus for a buck-boost converter is an output voltage control circuit capable of switching between a step-up mode and a step-down mode without a step-up/step-down mode, as disclosed in JP2010-158144 A.
In the case where two primary switches supplied with an input voltage in the buck-boost converter are both N-type transistors, a high-side switch of the primary switches is not driven unless a voltage greater than or equal to the input voltage is applied to the high-side switch. Accordingly, a capacitor for driving the high-side switch may be provided to supply the charge stored in the capacitor to drive the high-side switch.
In such a case, the charge in the capacitor decreases when the high-side switch is turned on. To turn on the high-side switch again, the capacitor needs to be charged while the high-side switch is off.
One possible method is as follows: a control signal for switching the buck-boost converter is forcibly turned off to provide a time period for charging the capacitor. Such a method, however, changes the switching frequency of the buck-boost converter. This can lead to problems such as increased gate charge loss of the transistors, decreased power conversion efficiency of the buck-boost converter, and noise.